• # General Mathematics Puzzles-2: Fun for all

About a fortnight ago, I posted a mathematics puzzle-1 and seeing the good response to that I am now posting the second one.

In mathematics, if there are two unknowns then we require two number of equations to solve it to find the value of these two unknowns. The normal way as how it is done is that first we make these two equations and then solve them using basic algebra.
My friend told me that he would solve a single equation containing two unknowns and gave me one interesting example.
He asked me to think about the children in a family and multiply the number of boys by 2 and add 5 to it. Then he asked me to multiply the result by 5 and then add number of girls to it and then tell the result to him. I calculated and told him that I got 58. He immediately replied that there are 3 boys and 3 girls in the family.
Can you find out how he did it?
• From the answer, you have given he removed twenty-five. The resultant number will have two digits. The digit in the tenths place is the number of boys and the number in the first place is the number of girls.

1 will explain with an example. I took the case of 4 boys and no girls.

As explained by your friend multiply the number of sons by 2 which will be 8(4X 2). Then add 5 to it. The number will be 13. Then multiply the same with 5. The resultant figure will be 65. For this, you have to add the number of daughters. In the example, I have taken the number of daughters is zero. So the figure I have to disclose is 65 to him. After telling the figure he will remove 25 from it. The resultant is 40. So the number of sons are 4 and no daughters.
This logic will work as long as the number of boys and girls are less than ten individually. If they are ten are more the logic may not work. For example, if you take 10 boys and 10 girls and follow the sequence given by your friend you will end up with the number 135. If we deduct 25 from it the resultant figure will be 110. The same number will come when you take 11 boys and 0 girls. when your friend says 10 and 10. You can say no it is 11 and 0. If he says 11 and 0. You can say no it is 10 and 10. I like to know the comments of the author.

drrao
always confident

• You are right Dr Rao. These puzzles are just for amusement and fun. It is expected that people will generally think a few boys and a few girls only. The main idea is to tell two unknowns from one equation.
Knowledge is power.